Crosslinked medium- to extra-high voltage power cables are predominantly made from low density polyethylene (LDPE), and the compositions need to exhibit sufficiently high melt extensional viscosity for sag-resistance during extrusion. This property is affected by the molecular architecture (molecular weight and polydispersity) of the LDPE. However, this approach often requires the use of different grades of LDPE. Another concept (employed with flexible ethylene-propylene rubber (EPR) cables) is to use clay as a filler to enhance sag-resistance, but the resulting dissipation factors are very high. It is desirable to identify additive approaches for enhancing melt extensional viscosity of LDPE during cable extrusion, with dissipation factor remaining satisfactorily low.
WO 2015/009562 teaches a composition comprising in weight percent based on the weight of the composition:                (A) 60-95% of an ethylene polymer of crystallinity of less than 40 percent;        (B) 4 to less than 40% of a propylene polymer with an upper melting point of greater than or equal to (≥) 130° C.; and        (C) ≥0.5% peroxide;with the proviso that the ethylene polymer either comprises a continuous phase (matrix) within which the propylene polymer is dispersed or is co-continuous with the propylene polymer. This teaching, however, does not disclose that the ethylene polymer is LDPE with a crystallinity of greater than 40%, and that as little as 1% of the propylene polymer in the composition is sufficient to enhance melt extensional viscosity at extrusion conditions, while minimizing any increases in flexural modulus and/or melt shear viscosity of the resulting composition.        